Search for BSM Higgs at the Search for BSM Higgs at the TevatronTevatron

Anton AnastassovAnton Anastassov(Northwestern University)(Northwestern University)

For the CDF and DFor the CDF and DØØ Collaborations Collaborations

Aspen 2008 Winter Conference: "Revealing the Nature of Electroweak Symmetry Breaking"

January 15, 2008

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BSM Higgs Searches• Look for particles consistent with the expected

physical manifestation of extended Higgs models:– 2HDM, Higgs triplets– Add SUSY a range SUSY models– Little Higgs models– …anything that goes beyond the SM Higgs

• Production/final states may be:– Unique to the BSM models– Similar to SM, but with modified production

rate/BR’s

Many search possibilities, but… finite manpower the CDF and DØ programs concentrate on:• Modes/models seen as most promising at the

Tevatron• Final states that can be efficiently triggered on

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The Tevatron Collider and Detectors

CDF and D0:• General purpose detectors, axial and

forward-backward symmetric• Precision tracking (incl silicon detectors)• Hadronic and EM calorimeters• Muon chambers• TOF systems

Recorded more than 3 fb-1 / experimentof quality data

(results in this presentation use up to 1.8 fb-

1)

p p collisions at s 1.96 TeV

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The tools of the searchesThe searches described in the

following rely on good particle identification:

• Electrons• Muons

• B-jets

• Photons

• Taus (hadronic decays)

•Very well understood•Use characteristic energy in the EM and HAD calorimeters; hits in the muon chambers ()•Easily accessible standard candles (Z, W)

(see J. Zhu’s presentation on EW results at the Tevatron)

•Displaced secondary vtx associated with the jet•Probability of tracks in the jet not originating from the IP•Soft leptons (e, ) in jets•Wealth of information apply multivariate techniques

(see Weiming Yao’s talk for detailed discussion)

•Energy deposition in the EM calorimeter

not associated with a track•Shower shape to discriminate against 0’s

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Tau Reconstruction (hadronic decays)Two-cone algorithm for

tracks and 0’s:– Common axis:

direction of a “seed” track Signal cone reconstruct Isolation annulus implement jet veto

phad(p ,E)

g/q

NN selection• Variables:

– Shower Profile– Calorimeter, track isolation– Charged fraction– Opening Angle– etc.

• Define 3 types:– -like, -like, multi-pion

Spectrum of taus from Z afterbackground subtraction

Spectrum of taus from a W sample

Similar reconstruction/misidentification rates at CDF and DØ

Review of Direct BSM Higgs Searches

at CDF and DØ

– Doubly-charged Higgs– Fermiophobic Higgs (hf)– MSSM Higgs (CP-conserving)

• Charged• Neutral

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Searches for H±±

• H±± predicted Higgs triplet, L/R symmetric models

• H++ can be light: ~100 GeV• DY-like H++H-- pair production• Decays to same/different-flavor

leptons

Detection modes:• 4 identified leptons• 3 ID’d leptons (+ 1 missed)• Use of tight/loose ID

• Most resent Tevatron search: DØ: H±± (1.1 fb-1)– Exp (obs): 3.1 (3) events mL(R)>150 (126.5) GeV @ 95% CL

• Previous searches from CDF (200-350 pb-1): ee, e, , e,

mL>114, 112 GeV @ 95%

CL • All Tevatron searches are statistics limited• Will benefit significantly from the full data samples

After adding H±± the Tevatron will cover all decay

modes

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Search for Fermiophobic Higgs

Searches for hf in Run II (1.1 fb-1)

• +X final state: ppVVhf+X , pphf W(Z)

mhf>90 GeV @ 95% CL (assuming SM couplings)

• +X final state : pp hfH± hf hfW± (suppressed VVhf couplings)

– possible in 2HDM for mhf<90 GeV, mH±<200 GeV, tan>1

– Favorable conditions: BR(H±hfW± ), BR(hf)≈1

Nbg=1.1±0.2, Nobs=0 xBR(H±hfW±)xBR(hf)2<25.3 fb @ 95% CL

(mass limit depends on assumed model)

• Fermiophobic Higgs:– Suppressed couplings to fermions

– Searches for hf• LEP II: mhf>108.3 GeV @ 95% CL (assuming SM couplings)

• Tevatron Run I: qq’V*hfZ , mhf>78.5 (82) GeV @ 95% CL DØ(CDF)

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Minimal Supersymmetric Standard Model (MSSM): SUSY extension of the SM with minimal particle

content

• Requires two Higgs field doublets• Five physical states: H, h, A; H±

• Lightest Higgs (h) mass close to EW scale• At tree level defined by mA and tan = vu/vd

• A couplings to b, enhanced by ~tan• But… complicated picture when radiative corrections

are included, dependence on additional parameters: consider “benchmark scenarios”:

Searches for MSSM Higgs

MSUSY M2 XtOS mgluino

mhmax 1 TeV

±200 GeV

200 GeV 2 MSUSY 0.8 MSUSY

no-mixing

2 TeV±200 GeV

200 GeV 0 0.8 MSUSY

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Search for Charged MSSM Higgs

• H modifies top BR’s (mostly at large and small tan• W± and H± decay modes differ: take advantage of different topologies in tt final states

H from t→bH+ is the most accessible mechanism at the Tevatron(can probe mH < mt-mb)

Expected number of events in the SM and MSSM for four topological final states (Lint = 192 pb-1)

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Search for Charged MSSM Higgs

Final state bg events SM exp data

2ℓ + jets 2.7±0.7 11 13

ℓ+ jets (1b) 20.3±2.5 54 49

ℓ + jets (≥2b) 0.94±0.17 10 8

ℓ + had + jets 1.3±0.2 2 2

Exclusive H± search (Lint=335 pb-1)

• Final state: e(++b + X

• Nbg=3.9±0.5, Nobs=6

Combined analysis of 4 final states

Measurement of R=l+jets/ll (1 fb-1)

• R=1.21±0.27 consistent with the SM

• H± exclusion assuming BR(H±cs)=1BR(tbH±)<0.35 @ 95% CL

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Neutral MSSM Higgs production

Higgs decays:– bb (~90%)

– (~9%)

Hbb Hgg

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Neutral MSSM Higgs

• For large tan h or H are almost mass degenerate with A, similar couplings

• The other one is SM-like, low-mass (m<135 GeV)

• Production and decays are affected by radiative corrections *

• The bb channel is more sensitive to these corrections (and therefore to the SUSY specific scenarios), while the channel is more robust

* M. Carena, S. Heinemeyer, G. Weiglein, and C.E.M. Wagner, Eur.Phys.J. C45 (2006) 797-814

9)1(

9

)1(

tan)()()(

22

2

bbSMAbbbbABRAbb

9)1(

tan),()(),(

2

2

bSMAggbbABRAggbb

b is a function of SUSY parameters

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Neutral MSSM Higgs Decaying to bb

• Look for associated production with b(b): suppress multi-jet backgrounds– Have to pay a price

• Require at least three b-tagged jets• Look for signal evidence in the mass

of the two highest-ET jets

Biggest challenge: predict bg, shape

• Apply mistag rates to bbj events to determine shape• Normalize (outside of signal region) to the observation• Check the predicted shape using MC multijet events

(flavor composition fixed to theoretical predictions)

• Use MC to get shapes and biases for different flavor composition

• Create 2D templates: di-jet mass vs mdifftag discriminating

variable (mdifftag = m1

tag+m2tag-m3

tag )

• 2D fit of mjj and mdifftag used to extract signal and

determines bg flavor composition

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Neutral MSSM Higgs Decaying to bb

Di-jet mass distribution of the two highest-ET jets

in the DØ search (triple b-tagged events)

The data are consistent with SM expectation.

Extracted limits (Lint=0.9 fb-1)

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Neutral MSSM Higgs Decaying to bb

Extracted limits (Lint=0.98 fb-1)

2D fit results, projections on the two variables.

The data areconsistent with SMexpectation.

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Neutral MSSM Higgs Decaying to

e, , had are shorthand notations for →e, →, and →hadrons , respectively.

Final state signatures are determined by the tau decay modes

Channels used in the presented searches:

6% e

23% ehad

3%

41%,

hadhad

23%, had

3% ee

Advantages of the Higgs mode: Lower bg’s compared to bb, probe all production modes Weaker dependence of sensitivity on SUSY parameters: more robust

ehad had e(1.8 fb-1)

had (1 fb-1) previous result also used ehad ebeing updated

Major backgrounds in Higgs : – Z(dominant)– Bg’s from jet fakes: multi-jet, W+jet(s), +jet(s) (ehad only)– Zee, Z, tt, other (small)

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Neutral MSSM Higgs Decaying to• Not enough info for full m reconstruction

• Approximation: project ET onto vis decay products (discussed later)

Higgs/Z separation:CDF: Use partial “mass”:

DØ: Form a NN using mvis and other event variables

),,( Em hadlvis

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Neutral MSSM Higgs Decaying to

mvis (GeV/c2) mvis (GeV/c2)

mvis (GeV/c2)mvis (GeV/c2)

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Exclusion Limits @ 95% CL

Interpretation of the limits

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Neutral MSSM Higgs: Near Future at CDF and DØ

• Utilize the full data samples• Multivariate signal selection• Separate treatment of events

with associated b-quark (for )

• Use full mass reconstruction (when possible)

Fully reconstructed m at CDF • Use collinear neutrino

approximation• Subset of selected events• No special optimization for

these plots

Previous DØ result from the exclusivesearch for )()( bbbbpp

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Summary

• Contrary to some rumors… CDF and D0 have not observed a Higgs signal yet

• However, diverse (and demanding) research programs are being actively pursued– Future progress depends on both

• Efficient utilization of the larger available samples • Improved analysis techniques

• Following the established pattern, expect updated results at the coming winter conferences